Different mil mod

[choi0706]

so my buddy made one for me.. same as what charlie said should work.. putting it on this weekend..

[hatchy]

What's the theory of operation?

[charliex]

matches the square wave of the o2 sensor

[choi0706]

if this works, and it should my buddy might make a few if anyone wants..

[Phantom]

This would be a huge breakthrough in my opinion- I have a new Elise with Arqray dual muffler- When I learned Sector111 is out of the decat tubes, I cancelled my order for one- I have been concerned about the o2 sensor issue (new car, warranty, check engine light, etc.), and with Sector111 not having stock, I'm going to see what happens with this issue- Please keep us posted- Thanx

[choi0706]

no problem! I hope this is the fix everybody is hoping for..

[hatchy]

Charliex, does this sit in between the rear sensor and the ECU, or does it replace the sensor? Do you know if this works with any other cars? I've had a hell of a time with my Suby...

[choi0706]

okay guys.. So far it works.. Put on 60 miles today and it runs good!.. I need to work out the wiring because I tapped the ecu for the ACC power.. Not very efficient but it works.. I will post pictures on sunday night.. Be ready to see something you've never seen on a elise..

[choi0706]

one more thing.. With this mil mod, i dont even have to plug in the second o2 sensor.. Probably i can just do away with it completly..

[charliex]

hatchy, there maybe a scooby version on the website i linked, it will replace the sensor, you might need a resistor mod as well for some cars.

glad to hear its working so far.

as for doing away with the second O2, stick an LM1 wideband in there instead

i've got another one that lets you change the mixture of the first o2 sensor too

[choi0706]

http://www.elisetalk.com/forums/showthread.php?t=22570

[hatchy]

I picked up the parts at the local electronics store today, I'll see if I have time to put it together this weekend. Did you build yours based on this: http://www.mkiv.com/techarticles/oxy...sor_simulator/ or did you change some of the resistor values? thanks

[choi0706]

pretty much stayed the same.. if mine works, these will be made available for everyone.. my friend needs gas money..

[charliex]

which pn 555 is he using

[choi0706]

no idea...^

[®ob]

Almost all 555s are the same. Ratshack should carry them

[choi0706]

so far all is good.. almost 300 miles no light yet..

[eliseowner2b]

these will be made available for everyone.. my friend needs gas money..

Any idea how many tanks of gas one of these is going to cost?

[charliex]

Originally Posted by ®ob

Almost all 555s are the same. Ratshack should carry them

similar in operation, but temperatures vary as well as operating paramaters, enough to have to redesign the circuit, i'm curious about the exhaust temp and it helps to have to exact modem he's verified works.

they are from radio shack.

Any idea how many tanks of gas one of these is going to cost?

they cost around $10-$20 in parts

[kverges]

I think the theory of operation of these devices is as follows. First, the primary or upstream O2 sensor dithers back and forth between about 0.5 and 0.9 volts, as the engine goes lean and rich relative to stoichiometric 14.7:1. A traditional O2 sensor is very sensitive around 14.7:1, but also very nonlinear. So it makes a very square-wave like signal. I also think the ECU deliberatly richens and leans the mixture as part of the feedback system to make the signal dither.

The catalytic converter oxidizes the excess hydrocarbons that are introduced when even slightly rich. The downstream O2 sensor measures a slight rich/lean transition, too, but it is at a different phase and frequency than the upstream signal, since the cat affects the oxygen content as it does its job. Earlier O2 sims could simply make a signal that oscillated between about 0.5-0.9V at a fixed frequency and that was good enough. Many more modern ECUs (and the Lotus ECU may be one) look not only for an oscillating signal, but for a difference from the primary O2, as the difference is an indication of the function and health of the catalytic converter. I have not recearched Federal requirements, but it may be necessary for more modern ECUs to monitor cat health.

What I do not know is the expected phase and/or frequency difference between the primary and secondary O2 sensor signals - this may also vary from car to car.

So that's about all I know. What I can't tell is whether this circuit makes a fixed signal or integrates the primary O2 sensor signal to make a variable signal of if it is even necessary. I have never built a sim either, just bought 'em. Kudos to charlie for sorting out the details. I have a commercial O2 sim on my car that works as far as I can tell, but the Lotus O2 ECU is pretty clever and keep an eye on it and plenty of miles to be sure the sim is working.

FWIW, the sims I currently use need an O2 sensor input and the O2 sensor must be in the exhaust flow, so I beleive they alter the O2 sensor signal.